One of the most difficult aspects of geophysical exploration has, from the early effort in the field, been the analysis and evaluation of data about subsurface formations in the earth. Drilling a hole in the earth to depths at which oil or gas can be expected to exist is a very expensive process. Thus, much effort has gone into the study of techniques to gain information about what exists below the surface in an effort to predict where deposits of interest might be found, and to predict the most profitable regions where bore holes can be drilled.
One of the most significant of these techniques is in the field of seismology in which acoustic energy is transmitted into the earth and reflections are received from the interfaces between strata. Normally, acoustic energy is produced at or near the surface and the reflections are received by an array of geophones arranged in a line or some other array. There are various techniques for repeatedly relocating the source and the geophones to produce, at the geophones, reflection energy which can be recorded and analyzed. Much work has been done to improve the data processing techniques and analysis to mimimize noise and to emphasize characteristics representative of subsurface formations, and also in the areas of identifying not only differences in velocity through various strata but also indicating the differences in velocity between adjacent strata in terms of ratios. Workers in the field have learned how to correct and strengthen the information received, and the reliability of the information has increased dramatically in recent years.
There remains, however, the problem of making sense out of the processed data after all of these corrections have been made. In the final analysis, a geophysicist or geologist must somehow look at the data and, using his training and experience, determine the significance of the information which has been received and processed. An experienced geologist commonly looks at a series of diagrams formed from the data, commonly constituting lines which "wiggle" across a sheet of paper and determine what these lines mean as far as the liklihood of hydrocarbon deposits is concerned. Graphical presentations in which sections of the data are shaded or colored have been produced to help him with this analysis, i.e., to help him visualize the subsurface formations and their interrelationships.
There have been several efforts to devise techniques for producing three dimensional representations of a subsurface region to assist with this visualization. Examples of these are found in the following documents.
U.S. Pat. No. 3,434,568--Caldwell PA1 U.S. Pat. No. 3,484,740--Cook PA1 U.S. Pat. No. 3,539,981--Sattlegger PA1 U.S. Pat. No. 3,638,178--Stephenson PA1 U.S. Pat. No. 3,668,619--Dennis PA1 U.S. Pat. No. 3,931,609--Anstey PA1 U.S. Pat. No. 4,030,064--Elliott PA1 U.S. Pat. No. 4,032,912--Wood PA1 U.S. Pat. No. 4,063,216--Chapman et al PA1 U.S. Pat. No. 4,078,177--Tiemens PA1 U.S. Pat. No. 4,210,964--Rogers et al PA1 U.S. Pat. No. 4,241,429--Bloomquist et al
Recently, an additional technique has been devised in which charts are made of horizontal slices through the earth, in successive planes, the information having been derived from seismic information which is normally presented as being representative of vertical slices through the earth. The technique involves manually constructing, from depth information given in the vertical sections, reflection information about horizontal sections. Thus, a sequence of still pictures representing horizontal slices is produced, and these horizontal sections are photographed on successive groups of frames of motion picture film (or on video tape) and the result is projected or displayed in the form of a motion picture. This technique is somewhat similar to certain techniques for producing animated cartoons in which a sequence of still pictures, when sequentially photographed and projected, gives the illusion of motion. Thus, the viewer has the ability to "look" at successive layers of subsurface formations, in sequence, and can better visualize the changing shapes of formations as depth increases.
Unfortunately, the process of producing the sequence of horizontal slices is extremely time consuming, laborious and expensive, and the effect of the final product leaves something to be desired because the resolution is not sufficiently good to permit seeing relatively small changes, and the movement from one image to the next is jerky because the data points are not sufficiently close together to permit the images to sequentially blend into each other. Because of the fact that the information is manually transferred from one coordinate system to another, and the result is then photographed, the resolution is seriously degraded, and many features are not visible or detectable at all.